public class Solution {
    public String reverseWords(String s) {
        s = s.trim();

        List spl = split(s);
        StringBuilder sb = new StringBuilder();

        for(int i = spl.size() - 1; i >= 0; i--) {
                sb.append(spl.get(i));
                sb.append(" ");
        }

        if ( sb.length() > 0 ) {
            sb.deleteCharAt(sb.length() - 1);
        }

        return sb.toString();
    }

    public static List split(String string) {
        int old_posn=0,posn=0;

        List str = new ArrayList();

        while (posn >= 0)
        {
            posn = string.indexOf(' ',old_posn);
            String next_word = (posn>0) ?
                    string.substring(old_posn,posn):
                    string.substring(old_posn);

            if (!next_word.isEmpty()) {
                str.add(next_word);
            }

            old_posn = posn + 1;
        }

        return str;
    }
}